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<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>XMLHTTPRequest通信</title>
    <meta name="description" content="">
    <meta name="viewport" content="width=device-width, initial-scale=1">
</head>

<body>
    <!--[if lt IE 7]>
            <p class="browsehappy">You are using an <strong>outdated</strong> browser. Please <a href="#">upgrade your browser</a> to improve your experience.</p>
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    <script>
        var xhr = new XMLHttpRequest();
        xhr.open("GET", "./3.test-data.txt", true);

        xhr.onreadystatechange = function () {
            if (xhr.readyStatus === 4) {
                if (xhr.status === 200) {
                    console.log(xhr.responseText);
                }else {
                    console.log(xhr.statusText);
                }
            }else {
                console.log(xhr.statusText);
            }
        }
        xhr.onerror = function (e) {
            console.log(xhr.statusText);
        };
        xhr.send(null);
    </script>
</body>

</html>